1. Field of the Invention
The present invention relates to electromagnetic reciprocating fluid pumps used in medical, refrigeration, environmental, automotive and other industrial applications.
2. Description of the Prior Art
Electromagnetic reciprocating pumps, also called solenoid pumps or linear pumps for use in medical, refrigeration, environmental, automotive and other industrial applications, have been known in the prior art. This type of pump, described for example by Mikiya et al. in U.S. Pat. No. 5,340,288, uses a piston-in-cylinder approach. In this approach, a reciprocating ferromagnetic piston is placed inside the bore of a cylinder. Check valves direct the flow of fluid, and an electromagnet is used to cause the ferromagnetic piston to reciprocate. But such a piston-in-cylinder approach has several problems associated with it. Because the piston is dimensioned to seal the cylinder bore in cooperation with a piston ring or a clearance seal, there is always a tendency for the piston and ring to contact and rub against the bore of the cylinder. The rubbing of the reciprocating piston and/or its ring against the bore, causes a substantial amount of wear on the piston, ring, and cylinder bore. As a result, the life of the pump will be limited. Further, such pumps are usually equipped with a coil spring for returning the piston to its original position after it has been displaced by the magnetic force exerted by the electromagnet. Such springs are subject to failure from metal fatigue induced by the continual flexing of the coils, thus introducing an additional source of possible mechanical failure and consequently reducing the life and reliability of the pump. Other prior art documents also show this type of electromagnetic reciprocating pump.
U.S. Pat. No. 5,330,330, issued to Kuwabara et al., and U.S. Pat. No. 5,222,878, issued to Osada et al., show pumps which use an electromagnet to cause reciprocating movement of a piston.
Pumps using a flexible diaphragm to replace the reciprocating piston, in order to reduce the sources of potential mechanical failure, have been proposed in the prior art.
U.S. Pat. No. 3,381,623, issued to Elliott, shows a pump that is electromagnetically actuated. The Elliott pump has a paramagnetic diaphragm which is moved by the action of an electromagnet.
U.S. Pat. No. 4,015,912, issued to Kofink, shows automotive fuel pump that is electromagnetically actuated. The Kofink pump has a tubular core through which a rod attached to the diaphragm passes.
U.S. Pat. No. 4,786,240, issued to Koroly et al., shows an artificial heart with an electromagnet housed in the diaphragm separating the chambers of the heart.
U.S. Pat. No. 4,915,017, issued to Perlov, shows a pump that uses a bi-stable circular diaphragm. In one embodiment a ferromagnetic core is embedded in the diaphragm and is used to initiate movement of the diaphragm.
U.S. Pat. No. 5,011,380, issued to Kovacs, shows an electromagnetic left-ventricular assist device which has a magnet attached to its diaphragm.
Pumps using diaphragms however, still suffer from certain drawbacks. In these pumps, the reciprocating piston is replaced with a flexible ferromagnetic diaphragm. This diaphragm is attached to the casing at its outer periphery and is positioned to face the electromagnet's poles. In this configuration, while vibrating, a diaphragm sweeps only a conical shaped space and hence offers a significantly smaller swept volume compared to a same sized reciprocating piston pump. As a result the flow rate, at a given vibration frequency, will be smaller relative to a same sized reciprocating piston pump. In addition, the large deflections cause large bending stresses in the diaphragm. These bending stresses are cyclic in nature and limit the fatigue life of the diaphragm.
Some of the prior art pumps, such as U.S. Pat. No. 1,927,617 issued to Schmidt, U.S. Pat. No. 2,669,937 issued to Presentey, and U.S. Pat. No. 3,819,305 issued to Klochemann et al., use a flexure/piston combination to prevent the friction and wear normally associated with piston rings. In this type of pump, a flexible annular ring-shaped diaphragm (called a flexure) is attached to the outer periphery of the reciprocating piston, obviating the need for sealing rings around the piston. However, such a flexure/piston approach also has several disadvantages. A large linear movement of the piston, needed to obtain high flow rates, creates large bending stresses in the flexure. These large bending stresses are typically several tens of thousands of pounds per square inch in magnitude and reduce the fatigue life of the flexure. In addition, the flexure has to be provided with several holes, used for clamping the flexure to the casing, which raise the stresses even further. Further, because flexures tend to impart a wobbling motion to the reciprocating piston, the reciprocating piston executes a complex cocking motion that is different from straight-line motion. The fatigue life of the flexure is further reduced as the flexure is forced to periodically conform to this complex cocking motion.
Other prior art pumps use a flexible diaphragm clamped between the pump chamber and the crankcase forming a leak-tight seal between the two. A rotating eccentric driven by a motor then causes the reciprocating motion of a piston which in turn causes the reciprocating motion of the diaphragm. Check valves control the flow into and out of the pumping chamber. The article "Guidelines for Selecting Small Pumps", by Eric Pepe, appearing in Machine Design, published by Penton Publishing Company of Cleveland, Ohio, 1991, shows a typical diaphragm compressor or pump in which a piston acts directly on the diaphragm.
Also known in the prior art are pumps that use a hydraulic drive to cause the reciprocating motion of a metallic diaphragm. The metallic diaphragm in this type of pump isolates the process fluid from the hydraulic fluid within the pump chamber, effectively partitioning the pump chamber into a hydraulic fluid side and a process fluid side. The reciprocating action of the diaphragm is developed by a reciprocating piston driven by a motor. The piston reciprocates in a cylinder that is part of a hydraulic circuit which includes the hydraulic fluid side of the pump chamber. The reciprocating movement of the piston causes hydraulic fluid to move into and out of the hydraulic fluid side of the pump chamber, thus imparting reciprocating movement to the diaphragm. Product literature entitled "Diaphragm Compressors", by Burton Corblin North America Inc. of Horsham, Penn., bulletin HP-400 entitled "Diaphragm Compressors", by Pressure Product Industries Inc. of Warminster, Penn., and bulletin 3.1 entitled "Metal Diaphragm Compressors", by Fluidtron Inc. of Ivyland, Penn., show typical hydraulically driven diaphragm fluid moving machinery.
These mechanically driven diaphragm pumps also suffer from the drawback of having too many moving parts leading to a great number of sources of potential mechanical failure.
Other examples of devices using electromagnets to drive a diaphragm have been disclosed in prior patents, however none disclose the unique elastomeric spring used in the pump of the present invention.
U.S. Pat. No. 2,230,273, issued to Smith, shows a submarine acoustic device having a metal diaphragm vibrated by an electromagnet.
Another example of an electromagnetic pump is shown in U.S. Pat. No. 5,286,176, issued to Bonin. The Bonin pump uses electromagnetically driven rollers to squeeze fluid along a flexible tube disposed between the rollers and an arcuate housing.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.